KR101047675B1 - Optical information reproducing device - Google Patents

Abstract

The information recording medium 21 of the optical information reproducing apparatus of the present invention includes a recording unit 3 capable of recording information in three dimensions and provided with a track, and a plurality of tracks along the track in a mark length recording method. Record marks are formed to record information. In the case where the track direction is the longitudinal direction with respect to the recording mark and the direction perpendicular to the track direction is the horizontal direction, in the present invention, the longitudinal length is larger than the transverse length with respect to the recording marks located on substantially the same plane. The total area of the recording marks of elongated shape is larger than the total area of recording marks other than the elongated shape. The optical information reproducing apparatus of the present invention further includes a first light source 20a for emitting the reproduction light 22b having a wavelength λ ₁ , an objective lens 6 for condensing the reproduction light to the recording unit, and a recording unit from the recording unit. A first photo detector 19a for detecting a reproduction signal from the reflected light is included. The condensed reproduction light includes, as a main component, a polarization component that polarizes in a direction perpendicular to the track direction. The track pitch of the recording unit is 1.3 times or less the wavelength λ ₁ of the reproduction light.

Description

Optical information reproduction device {OPTICAL INFORMATION REPRODUCTION DEVICE}

The present invention relates to an optical information reproducing apparatus for reproducing information from an information recording medium capable of recording information three-dimensionally.

An optical information reproducing apparatus is a device for reproducing information recorded on an information recording medium such as an optical disc or an optical card memory such as a CD (Compact Disk) and a DVD (Digital Versatile Disk). There is also provided an apparatus which further includes a function of recording information on such an information recording medium (hereinafter, an optical information reproducing apparatus may be referred to as an optical information recording and reproducing apparatus).

In order to realize a larger capacity, an information recording medium having a multilayer structure in which a plurality of recording layers are stacked is provided as an information recording medium capable of recording information three-dimensionally. In Fig. 7, an example of a conventional optical information recording and reproducing apparatus including such a multi-layered information recording medium is disclosed (see Non-Patent Document 1, for example).

In the information recording medium 121 shown in FIG. 7, the recording unit 103 is provided on the glass substrate 104, and the recording unit 103 alternates between the recording layers 101a-101d and the intermediate layers 102a-102c. It is formed by laminating. That is, in the information recording medium 121, a plurality of recording layers are stacked in the optical axis direction (Z-axis direction in the figure) of the objective lens (objective lens 106 for condensing recording light or reproduction light in each recording layer). Because of this, three-dimensional information can be recorded.

In the conventional optical information recording and reproducing apparatus shown in Fig. 7, the recording light source 120a and the reproduction light source 120b are provided. The recording light source 120a is a Ti sapphire laser. The recording light 122a having a wavelength of 790 nm and a large peak power emitted from the light source 120a passes through the beam splitter 118a, and the beam diameter is enlarged by the beam expander 123. In addition, a recording layer (the recording layer 101c in the figure) that passes through the beam splitter 118b and is intended for the information recording medium 121 having a multi-layer structure which can be recorded in three dimensions by the objective lens 106. Is focused on (converged light 107). The information is recorded by forming the recording pits 105 as recording marks in the recording layer 101c by using nonlinear absorption phenomena such as, for example, two-photon absorption phenomena occurring in the light collecting portion.

The reproducing light source 120b is a He-Ne laser. The reproduction light 122b emitted from this light source 120b and having a small peak power having a wavelength of 0.6328 µm is bent in the -Z axis direction by the beam splitter 118a, and thereafter, the same optical path as that of the recording light 122a. The light is condensed to the target recording layer (recording layer 101c in the figure) via the above. The light reflected by the recording pit 105 is bent in the Y-axis direction by the beam splitter 118b and condensed by the detection lens 111. A pinhole plate 114 having a pinhole is disposed at the condensing point of the detection lens 111, and the signal can be reproduced by detecting the light passing through the pinhole with the photodetector 119.

8 shows an XY plane perpendicular to the Z axis, and a recording pit 105 formed in one recording layer is schematically shown. In the figure, hatching is performed on the recording pit 105. In addition, the square shown by the broken line represents an unrecorded pit. The recording pit 105 is square, the mark length (shown as ML in the figure), which is the pit size in the Y-axis direction, is 0.5 占 퐉, and the track pitch (shown as TP in the figure) is 1 占 퐉. In the figure, the Y-axis direction represents the track direction, and the X-axis direction represents the direction perpendicular to the track direction.

As shown in Fig. 8, the recording of information in the conventional optical information recording and reproducing apparatus is a mark position recording in which information is recorded in the same size of the recording pit and whether or not the pit is formed. There is a mark length recording method as a recording method which can make the recording capacity larger per mark than this mark position recording. The mark length recording method is a method of recording by changing the length of a recording mark, and it is also possible to make the recording capacity more than twice as much as the mark position recording.

 [Non-Patent Document 1] Yoshimasa Kawada: "Three-dimensional Optical Memory Using a Femtosecond Laser", Optronics pp. 138-142 (2001)

However, in the above conventional apparatus, when reproducing the information recorded in the target recording layer (for example, the recording layer 101c shown in FIG. 7), the closer side (the light incident side, the objective lens 106) is reproduced. The recording pits formed in the recording layers 101a and 101b located on the side) cause diffraction loss of the converged light 107, resulting in loss of light and difficulty in reproducing information. In other words, when the number of layers in the near recording layer is large, it is difficult to reproduce information on a large-capacity information recording medium having a large number of layers because the light is attenuated excessively until it reaches the target recording layer. It was.

The optical information recording medium of the present invention includes a recording unit capable of recording information in three dimensions and provided with a track having a predetermined track pitch, and a plurality of tracks along the tracks of the recording unit in a mark length recording manner. In the case where the recording mark is formed, information is recorded, the track direction is set to the longitudinal direction with respect to the recording mark, and the direction perpendicular to the track direction is set to the transverse direction. , claim that the longitudinal length side is emitted to the lateral length of the larger of the long recording mark shape total area, the total area larger than the information recording medium of the recording mark has a shape other than the long shape, reproducing light having a wavelength (λ ₁₎ A light source, an objective lens for condensing the reproduction light emitted from the first light source to the recording unit of the information recording medium, and the reflected light from the recording unit. An optical information reproducing apparatus comprising a first optical detector for the optical detecting a reproduction signal and a track pitch of the information recording medium, and more than 1.3 times that of the reproduction light wavelength (λ _1), the reproducing light, the information And a polarization component which polarizes in a direction perpendicular to the track direction of the information recording medium when the light is collected onto the recording medium as a main component. However, the inclusion of a polarization component that polarizes in a direction perpendicular to the track direction as a main component means that the amplitude of the polarization component that polarizes in the direction perpendicular to the track direction is larger than other polarization components. In addition, the track referred to here is a configuration in which the track is virtually assumed as a path for recording the recording mark in a state in which the track groove is not formed and the recording mark is not formed in addition to the configuration in which the track groove is formed. We shall include.

The optical information reproducing apparatus of the present invention also includes an optical information recording and reproducing apparatus provided with a recording mechanism together with the information reproducing mechanism.

1 is a schematic diagram showing a basic configuration of an embodiment of an optical information reproducing apparatus of the present invention, and a state in which light propagates;

FIG. 2 is a schematic diagram showing recording marks recorded on an information recording medium included in the optical information reproducing apparatus shown in FIG. 1;

FIG. 3 is a diagram showing the relationship between the transmittance per recording layer per layer of the information recording medium and the thickness of the recording layer in one embodiment of the optical information reproducing apparatus of the present invention;

FIG. 4 is a diagram showing the relationship between the transmittance per recording layer per layer of the information recording medium and the thickness of the recording layer, according to another embodiment of the optical information reproducing apparatus of the present invention;

FIG. 5 is a diagram showing the relation between the transmittance per layer of the information recording medium and the thickness of the recording layer, according to another embodiment of the optical information reproducing apparatus of the present invention; FIG.

6 is a schematic diagram showing a basic configuration of another embodiment of the optical information reproducing apparatus of the present invention, and a state in which light propagates;

7 is a schematic diagram showing a configuration of an example of a conventional optical information recording and reproducing apparatus, and a state in which light propagates;

FIG. 8 is a schematic diagram showing recording marks recorded on an information recording medium included in the optical information recording and reproducing apparatus shown in FIG.

The optical information reproducing apparatus of the present invention, when reproducing information recorded in a mark length recording method on a recording portion of an information recording medium capable of recording information three-dimensionally, polarizes in a direction perpendicular to the track direction of the information recording medium. Light containing a polarization component as a main component (for example, linearly polarized light polarized in a direction perpendicular to the track direction or an elliptical polarization mainly composed of a polarized light component polarized in the direction perpendicular to the track direction) as reproduction light I use it. Further, the track pitch of the information recording medium is 1.3 times or less the wavelength λ ₁ of the reproduction light. When a row of recording marks formed on substantially the same plane in the recording unit is one recording surface (one recording layer), information for the purpose of reproduction is recorded by the reproduction light as in the apparatus of the present invention. Diffraction loss due to the recording mark of the recording layer located closer to the recording layer (light incidence side, objective lens side) can be reduced. As a result, even in an information recording medium on which information is recorded three-dimensionally, the information can be reproduced with a good SN ratio (S / N). In addition, even if the number of recording layers is large, information can be reproduced, so that the capacity can be increased by increasing the number of layers.

In the optical information reproducing apparatus of the present invention, the first light source may be configured to emit a reproducing light containing, as a main component, a polarization component polarized in a direction perpendicular to the track direction of the information recording medium, and the reproducing focused on the recording unit. An optical component for converting the polarization state of the reproduction light emitted from the first light source in the optical path between the first light source and the objective lens so that the light contains, as a main component, a polarization component that polarizes in a direction perpendicular to the track direction of the information recording medium. (For example, a wave plate) may be further included.

The optical information reproducing apparatus of the present invention may be an optical information recording and reproducing apparatus provided with a recording mechanism as well as a reproducing mechanism. In this case, the first light source may further be configured to emit the recording light, or may be configured to further include a second light source that emits the recording light. In the case of the optical information recording and reproducing apparatus, the objective lens can focus the recording light onto the recording unit included in the information recording medium, similarly to the reproduction light. At this time, the recording light focused on the recording unit may contain, as a main component, a polarization component that polarizes in a direction perpendicular to the track direction of the information recording medium. In addition, the wavelength λ _{1 of the} reproduction light and the wavelength λ ₂ of the recording light are different from each other, and by using the difference in wavelengths, the reproduction light focused on the recording portion is polarized in a direction perpendicular to the track direction of the information recording medium. The polarization state of the reproduction light emitted from the first light source and the first light source or the first light source in the optical path between the first light source and the objective lens such that the polarizing component An optical component for converting the polarization state of the recording light emitted from the two light sources may be further provided. This optical component is, for example, and substantially functions as an integral multiple plates of λ _1/2, i.e., λ _1/2 plate, λ ₁ plate, 3λ _1/2 plate or the like with respect to the reproduction light, and the recording light substantially it can be used for standing-wave plate functions to λ _2/4 plate. In addition, you may form a recording mark in a recording part using pulsed light as recording light, and nonlinear absorption phenomenon. In addition, the nonlinear absorption phenomenon in this specification is a phenomenon in which the absorption sensitivity of a recording part is not proportional to the energy of the irradiated light, For example, when there exists a threshold value in absorption sensitivity, an absorption sensitivity is a power of approximately 2 times of light energy. ), When two-photon absorption, or multi-photon absorption with approximately n-square characteristics (n is an integer greater than or equal to 3) occurs, when two-photon absorption or multi-photon absorption is triggered and plasma is generated, and combinations thereof It includes the phenomenon that occurs when it is. When information is recorded using the nonlinear absorption phenomenon in this manner, in order to realize higher density, it is preferable to make the wavelength λ _{1 of the} reproduction light shorter than the wavelength λ ₂ of the recording light.

 The optical information reproducing apparatus of the present invention may further include a pinhole plate provided with a pinhole in an optical path between the information recording medium and the first optical detector. The pinhole plate is provided with a pinhole having a diameter that allows light to reflect the target information contained in the reflected light. By arranging such a pinhole plate, detection of reflected light (unnecessary reflected light) from a recording layer different from the recording layer to be reproduced by the first photodetector can be suppressed, so that interlayer crosstalk can be reduced. Further, by setting the area of the light receiving portion provided in the first photodetector as the area for receiving the light reflecting the target information contained in the reflected light, the same effect can be obtained without passing the reflected light through the pinhole.

The optical information reproducing apparatus of the present invention is a second optical detector for detecting a focus / track error signal, and a focus / track error signal detection arranged in an optical path between the information recording medium and the second optical detector to split the reflected light. You may further include an element. At this time, when the pinhole plate is provided, at least one branched light branched by the focus / track error signal detection element is guided to the second photodetector without passing through the pinhole.

In the optical information reproducing apparatus of the present invention, when the recording mark formed on the information recording medium is void (details will be described later), the effect of the present invention is great. In addition, the recording mark may be a recording pit formed by using the refractive index change of the recording material.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings.

(Embodiment 1)

The optical information reproducing apparatus of Embodiment 1 of the present invention will be described in detail with reference to FIGS. 1 and 2. In addition, since the optical information reproducing apparatus of the present embodiment has a recording function in addition to the reproducing function, the optical information reproducing apparatus will be described below.

Fig. 1 is a schematic diagram showing the basic configuration of the optical information recording and reproducing apparatus according to the present embodiment and the state where light is propagated, and Fig. 2 is a recording mark formed on the information recording medium included in the same optical information recording and reproducing apparatus. It is a schematic diagram showing.

In the optical information recording and reproducing apparatus of this embodiment, two kinds of light sources are provided, a light source for recording (second light source) 20a and a light source for reproduction (first light source) 20b. The wavelength λ ₂ of the recording light 22a emitted from the recording light source 20a and the wavelength λ ₁ of the reproduction light 22b emitted from the reproduction light source 20b are different from each other. In the optical path from these two light sources 20a and 20b to the information recording medium 21, the beam splitter 18a, the collimator lens 16, the beam splitter 18b, the granular mirror 12, the wavelength The plate 10, the spherical aberration correcting element 13, and the objective lens 6 are arranged. The focus / track error signal detection element 15 and the detection lens 11 are provided in the optical path from the beam splitter 18b to the photo detectors 19a and 19b, which becomes a return path. Further, in the optical path between the detection lens 11 and the first photodetector 19a for detecting the reproduction signal, a pinhole plate 14 having a pinhole for reducing the interlayer crosstalk of the information recording medium 21 is disposed. have.

The information recording medium 21 is a three-dimensional recordable medium. The recording unit 3 and the protective layer 4 are provided on the substrate 9, and the protective layer 4 is optically used for recording and reproducing information. It is arrange | positioned so that it may be incident side. In the recording unit 3, recording layers 1a to 1d and intermediate layers 2a to 2c are alternately stacked. In the present embodiment, the recording unit 3 is formed of four recording layers and three intermediate layers, but the number of stacked recording layers is not limited thereto. In addition, the recording unit 3 does not necessarily have to be a multi-layer structure in which a plurality of recording layers are stacked, and it is only necessary to be able to record information three-dimensionally. For this reason, if the whole recording part 3 is formed in one recording layer like a so-called bulk structure, if this recording layer can record information three-dimensionally, there is no problem.

The recording layers 1a to 1d of the information recording medium 21 are made of a material whose refractive index changes due to thermal deformation at a predetermined temperature, for example, and the portion where the refractive index change has occurred is a recording pit (recording mark). (5). In FIG. 2, a row of recording pits 5 formed in each track is typically displayed for one of the plurality of recording layers constituting the recording unit 3 of the information recording medium 21. In this embodiment, each track in each recording layer has virtually no track groove, and is assumed virtually, and a track for recording each recording mark is used as a track. However, a track groove or the like may be actually provided. 2 shows only five tracks 23a to 23e, and hatching is performed on the recording pits 5 formed in each track. In the figure, the Y axis represents the track direction, and the X axis represents the direction perpendicular to the track direction. The recording pits 5 are formed by the mark length recording method, and the length in the track direction (length in the longitudinal direction) (in the drawing, denoted by ML. Hereinafter, the mark length may be described below). For example, step 7). The width (length in the lateral direction) of the recording pit 5 is constant. In FIG. 2, the track direction is a straight line extending in the Y-axis direction. However, when the information recording medium 21 has a disk shape, the track is a curve that becomes part of an arc. Therefore, when the information recording medium 21 has a disc shape, the X axis direction corresponds to the radial direction of the disc, and the Y axis direction corresponds to the tangential direction of the track provided on the disc.

In the information recording medium 21 of the optical information recording and reproducing apparatus of the present embodiment, the track pitch (denoted by TP in the figure) indicating the interval between adjacent tracks is the wavelength λ ₁ of the reproduction light 22b. 1.3 times or less, Preferably it is below the wavelength (lambda) ₁ of the reproduction light 22b. By setting such a track pitch, the transmittance of the recording layer can be made high. When the wavelength λ ₁ of the reproduction light 22b is 0.405 µm, for example, the track pitch can be 0.32 µm, for example. In this embodiment, the mark length of the recording pitch 5 is changed in seven steps, for example in the range of 0.149 micrometers-0.596 micrometers, and correspond to what is called a 2T-8T recording mark. The basic length T is 0.0745 μm. The width of the recording pit 5 can be half the track pitch, for example, 0.16 탆. In this case, the recording pit 5 of 3T-8T is a long shape (long shape in track direction) larger than the length of the horizontal direction in the longitudinal direction. Therefore, in each recording layer of the information recording medium 21, the total area of the recording marks having an elongated shape is larger than the total area of the recording marks having a shape other than the elongated shape.

In this embodiment, since information is recorded on the information recording medium 21 using nonlinear absorption phenomenon such as two-photon absorption phenomenon or multiphoton absorption phenomenon, the wavelength λ ₂ is used as the recording light source 20a. For example, a semiconductor pulse laser light source that emits pulsed light having a pulse width of 0.66 mu m and a pulse width of 100 femtoseconds to 10 nanoseconds is suitably used. On the other hand, a semiconductor laser light source that emits light having a wavelength λ ₁ , for example, 0.405 μm can be used for the reproduction light source 20b. By using a semiconductor laser as a light source, miniaturization and cost reduction are possible. When information is recorded using the nonlinear absorption phenomenon, the density λ ₁ of the reproduction light 22b can be made shorter than the wavelength λ ₂ of the recording light 22a to achieve higher density. This is because the recording pits formed by using the nonlinear absorption phenomenon can be made smaller than those recorded by normal recording. For example, when performing two-photon absorption recording at λ ₂ = 0.66 μm, the spot diameter can be made 1 / (2 ^1/2 ) times smaller than in the usual case, so that the normal diameter is recorded at a wavelength of substantially 0.47 μm. Same as the case. For that reason, the wavelength λ _{1 of the} reproduction light is shorter than the wavelength λ ₂ of the recording light, preferably about ₂ λ ₁ = λ ₂ / (2 ^1/2 ), so that it is about 2 than the case of λ ₁ = λ ₂ . The ship's density can be increased.

The information recording / reproducing apparatus of the present embodiment is configured such that when the light is collected on the information recording medium 21, the reproduction light 22b becomes linearly polarized light which is polarized in a direction perpendicular to the track direction of the information recording medium 21. . By reproducing the information recorded by the mark length recording method as described above using such linearly polarized light, even in the case where it is necessary to pass another recording layer until the target recording layer is reached, the diffraction loss of the light can be reduced. A playback signal can be obtained. In addition, the polarization state of the recording light condensed on the information recording medium 21 is not specifically limited, In this embodiment, the apparatus is comprised so that circularly polarized light may be.

The wavelength plate 10 is disposed in a common optical path between the recording light 22a and the reproduction light 22b between the objective lens 6 and the light sources 20a and 20b, but the recording light ( It is designed to be substantially 1/4 wavelength plate for or close to the wavelength λ ₂ of 22a), and is an integer multiple of an integer multiple of 1/2 for the wavelength λ ₁ of the reproduction light 22b, that is, 1 It is designed so that it may become / 2 wavelength plate, 1 wave plate, or 3/2 wave plate, or the like. This is for the reproduction light 22b to be linearly polarized and the recording light 22a to be circularly polarized light when it is focused on the information recording medium 21. The beam splitter 18a is also designed to transmit the recording light 22a and reflect the reproduction light 22b by using the difference in wavelength. The beam splitter 18b also uses a difference in wavelength to function as a polarizing beam splitter for the recording light 22a and a half mirror that hardly depends on the polarization direction for the reproduction light 22b. It is designed to function as.

Next, the recording method in the optical information recording and reproducing apparatus of the present embodiment will be described. As shown in Fig. 1, at the time of recording, the recording light 22a, which is a pulse laser light having a relatively high peak power by linearly polarized light emitted from the recording light source 20a in the Y-axis direction, is a beam splitter 18a. The light path is passed through the collimator lens 16 to become substantially parallel light, passes through the beam splitter 18b serving as the beam splitting element, and the optical path is bent in the -Z axis direction by the granular mirror 12. The recording light 22a bent in the -Z axis direction is substantially converted to the original light in the wave plate 10 and passes through the spherical aberration correcting element 13 (light shown by 8 in the drawing), for example. By the objective lens 6 having a numerical aperture NA of 0.85 and a focal length of 2 mm, it passes through the protective layer 4 of the information recording medium 21 and serves as a recording layer 3 as an object of the recording unit 3 (in FIG. The light condensed on the recording layer 1b) (hereinafter, the light condensed on the information recording medium 21 may be referred to as converging light 7), and nonlinear absorption such as a two-photon absorption phenomenon or a multi-photon absorption phenomenon. By using the phenomenon, a row of recording pits 5 as shown in FIG. 2 is recorded in the recording layer 1b.

Since the thickness of the recording portion 3 passing through the converging light 7 to reach the target recording layer differs depending on the recording depth of the recording pit 5, the objective lens 6 is separated from the recording light source 20a. When the spherical aberration correcting element 13 provided in the optical path up to) is recorded while controlling the spherical aberration amount according to the recording depth of the recording pit 5 to be recorded in the recording unit 3, the good recording pit 5 can be recorded. Can be formed. As the spherical aberration correcting element 13, a liquid crystal element having a variable refractive index distribution, a beam expander having a variable interval in the optical axis direction of both lenses as an actuator in combination with a concave lens and a convex lens can be used. .

For example, when recording using a two-photon absorption phenomenon, when a material that absorbs light having a wavelength that is half of the recording wavelength λ ₂ is used as the recording material, for example, it is relatively high in several 100 mW to several W or more. Irradiating recording light with a high peak power and a small pulse width of 100 femtoseconds to 10 nanoseconds has the same effect as having half the wavelength at the high power density portion (condensing point) of the light focused by the objective lens 6. Occurs, absorption occurs in the recording material, and the recording pits 5 are recorded. As such, absorption occurs only at the condensing point, so that light is not so attenuated even when recording is performed in the recording layer in the deep region. For this reason, the recording method using the nonlinear absorption phenomenon is suitable for a three-dimensional optical memory such as a multilayer memory.

In general, the recording pits 5 are recorded three-dimensionally by using the change of the optical constant of the recording layer 1, but in the present embodiment, the recording pits 5 are mainly recorded by using the change of the refractive index of the recording material. As the recording material, for example, a photopolymer, a dye such as diarylethene, a resin incorporating ultrafine particles made of zinc oxide (ZnO), and the like, TeO _2, and the like are suitable. have. Although the amount of refractive index change can be controlled by the recording light irradiation method, it is also possible to form hollow pits called voids by using pulsed light having a relatively high peak power of several W to several 10 kW. Also, to form a hollow pit is to form a hole in the recording layer. In the case of voids, since the refractive index is 1.0, when the refractive index of the recording material is 1.7, for example, the amount of change in refractive index is increased to Δn = -0.7. As a result, there is an effect that signals can be reproduced with high contrast. In the case where the recording layer is formed of a phase change material, since the recording is performed using absorption of light, the case where the number of recording layers is large is not suitable, but in the information recording medium having a multilayer structure of about 2 to 6 layers, It can be used as a recording layer.

Next, the reproduction method in the optical information recording and reproducing apparatus of the present embodiment will be described. At the time of reproduction, the reproduction light 22b, which is a linearly polarized laser light emitted from the reproduction light source 20b, is bent in the Y-axis direction by the beam splitter 18a, and is substantially parallel light by the collimator lens 16. The light path is transmitted through the beam splitter 18b, and the optical mirror 12 bends the light path in the -Z axis direction. The regenerated light 22b bent in the -Z axis direction passes through the wave plate 10 and the spherical aberration correcting element 13 (light shown by 8 in the figure), and is in the state of linearly polarized light. Is focused on the recording layer for the purpose of the recording section 3 of the information recording medium 21 (converged light 7). The reproduction light 22b condensed on the information recording medium 21 by the objective lens 6 is linearly polarized light which is polarized in a direction perpendicular to the track direction of the information recording medium 21. Specifically, when the reproducing light source 20b emits linearly polarized light that is polarized in parallel with respect to the track direction, the wavelength plate functions as a half wave plate with respect to the wavelength λ ₁ of the regenerated light 22b. (10) is provided and converted into linearly polarized light which is polarized in a direction perpendicular to the track direction. In addition, when the reproducing light source 20b emits linearly polarized light that polarizes in a direction perpendicular to the track direction, the wavelength plate 10 functions as one wavelength plate with respect to the wavelength λ ₁ of the reproduction light. By using, etc., linearly polarized light as mentioned above can be obtained. By using the light having such a polarization state as the reproduction light, when reproducing the recording pits 5 of the recording layer 1b, the diffraction loss by the recording pits 5 of the recording layers 1c and 1d on the near side is reduced. Can be reduced.

Further, in order to reduce the diffraction loss caused by the recording pit 5 formed in the near recording layer, it is preferable to reduce the thickness per recording layer. However, if the recording layer is too thin, the recording pit 5 becomes a signal of information. The reflectance from is lowered. For this reason, for example, when the refractive index of the recording material is 1.7 and the recording pits 5 are void, in order to obtain reflectances of 1% to 8%, the thickness per recording layer is preferably 0.02 µm to 0.05 µm. .

The light reflected by the recording pit 5 returns in the reverse direction, sequentially passes through the objective lens 6, the spherical aberration correcting element 13, the wave plate 10, and the granular mirror 12, and the beam splitter. The optical axis is bent in the Z direction by 18b, and the diffraction type focus / track error signal detection element 15 is diverged into a plurality of lights (however, in FIG. 1 for the sake of simplicity, the diffraction type focus / track error signal). In the optical path from the detection element 15 to the detection lens 11, the branched light is not shown.) The detection lens 11 forms converged light 17a and 17b. The rim intensity on the detection lens 11 is, for example, 0.8. The converged light 17a, which is the reflected light for obtaining the reproduced signal, passes through the pinhole provided in the pinhole plate 14, and the reproduced signal is detected by the photodetector 19a. The converged light 17b, which is a branched, focus / track error signal, is detected by another second photodetector 19b without passing through the pinhole. Since the converging light 17b serving as the focus / track error signal does not pass through the pinhole, the focus error signal and the track error signal can be detected by conventional methods such as astigmatism and three-beam tracking.

 The focal length of the detection lens 11 is, for example, 33 mm, and the diameter of the airy disk at the photodetector 19 is, for example, 9.6 μm. The pinhole plate 14 is provided so that the pinhole may be positioned at a substantially focal point position of the converged light 17a for detecting the reproduction signal. This is the light reflected by the other recording layers 1a, 1c, and 1d positioned above and below the recording layer 1b to be reproduced, that is, the recording pits of the recording layer separate from the recording pits of the recording layer to be reproduced. Since crosstalk (interlayer crosstalk) light, which is light reflected by unnecessary light (interlayer crosstalk), does not enter the pinhole, the light extending beyond the pinhole size has an effect of reducing interlayer crosstalk. In addition, instead of providing the pinhole plate 14, the same effect can also be obtained by using as a first detector 19a a micro-photo detector having a light receiving portion having a size of a pinhole diameter.

In this embodiment, the size of the pinhole is 5 times or less the diameter of the airy disk of the converging light 17a, so that, for example, a level without problem when the interval between adjacent recording layers is set to 5 to 8 占 퐉 (interlayer) It is possible to improve the quality of the reproduction signal up to crosstalk amount? If the size of the pinhole is made smaller, the gap between the recording layers can be made smaller. However, if the size of the pinhole is made too small, the amount of light entering the pinhole is reduced, or the optical system is deformed according to the environmental temperature so that the converged light 17a can deviate from the center of the pinhole. In some cases, it is necessary to consider these and determine the size of the pinhole.

As another example of the optical information recording and reproducing apparatus, the beam splitter 18b may be a half mirror that hardly depends on the polarization direction for either the recording light 22a or the reproducing light 22b, or the wavelength plate. It is good also as a structure which does not install (10). In this configuration, although the utilization efficiency of the recording light 22a is lower than that of the optical information recording and reproducing apparatus shown in FIG. 1, the effect of reducing the influence of birefringence that may occur in the information recording medium 21 can be obtained. Can be. In addition, also with respect to the recording light 22a, since it becomes a polarization direction with less diffraction loss, it becomes possible to suppress attenuation of the light intensity in the information recording medium 21.

Next, in order to explain the relationship between the polarization state of light and the diffraction loss, the change in transmittance of the recording layer with respect to the difference in the polarization direction of light will be described in detail. FIG. 3 shows the relationship between the transmittance per layer of the recording layer constituting the information recording medium 21 and the thickness of the recording layer, respectively, for two kinds of light having different polarization directions. Using a composite material containing about 55 wt% of fine particles of zinc oxide (ZnO) and about 45 wt% of polyester, a recording layer having a different thickness was produced, and the transmittance was measured for each recording layer. As fine particles of zinc oxide, those having a particle diameter of 30 nm or less were used. In the recording layer, recording marks were formed on tracks with a track pitch of 0.32 mu m. The recording mark here was a recording mark corresponding to 2T-8T, whose width was 0.16 µm and the mark length was changed in seven steps in the range of 0.149 µm to 0.596 µm. The recording mark was void, the refractive index of the recording layer in the portion where no void was formed was 1.7 and the refractive index of the void portion was 1.0. The light used here was Y-direction polarization (linearly polarized light polarizing in a track direction) and X-direction polarization (linearly polarized light polarizing in a direction perpendicular to the track direction), and both wavelengths were 0.405 micrometer.

When the transmittance of the recording layer was measured under the above conditions, it was confirmed that the X-direction polarized light had a larger transmittance than the Y-direction polarized light. According to this result, when the linearly polarized light polarized in the direction perpendicular to the track direction is used, the transmittance of the recording layer located closer to the recording layer to be reproduced can be maintained higher, so that the diffraction loss of the reproduction light can be reduced. I could see that. As shown in FIG. 3, for example, the transmittance per recording layer when the thickness was 0.035 μm was 97.5% in the X-direction polarization and 95.8% in the Y-direction polarization. In addition, the transmittance | permeability in the case of circular polarization is an average value of these two curves. For example, the transmittance when passing through 10 recording layers having a thickness of 0.035 µm is 77.6% and 65.1% for the X-direction polarization and the Y-direction polarization, respectively, and the transmittances when passing through the 20 layers are respectively. , 60.2%, 42.3%. As described above, it was found that the transmittance can be improved in a width larger than that of the Y-direction polarization. When the transmittance is improved, the diffraction loss of the light can be suppressed, so that the SN ratio of the signal in which the noise light is reduced and the amount of reproduction signal light is increased can be improved. As a result, it is also possible to further increase the number of layers of the recording layers to be stacked.

In addition, the transmittance per recording layer was similarly measured with respect to the case where the diaryl ethene which is a photochromic material was used for recording material, and the recording mark was made into the recording pit by a change of refractive index. Specifically, FIG. 4 shows the result of the case where the recording part is produced using the ultraviolet curable resin having a refractive index of 1.45 in the intermediate layer, and FIG. 5 shows the result of the recording part being produced using the ultraviolet curable resin having the refractive index of 1.40 in the intermediate layer. In addition, the refractive index of the portion where the recording mark was not formed was 1.55, the refractive index of the recording mark portion was 1.65, and the refractive index change amount Δn = 0.1. According to the results shown in FIGS. 4 and 5, even in the case where diarylethene is used as the recording material, it was confirmed that the transmittance of the X-direction polarization is higher than that of the Y-direction polarization.

In addition, as described in the present embodiment, the reproduction light 22b condensed on the information recording medium 21 is preferably linearly polarized light which is polarized in a direction perpendicular to the track direction of the information recording medium 21. Almost the same effect is acquired also in elliptical polarization which contains as a main component the polarization component which polarizes to the direction perpendicular to a direction.

As described above, information is recorded by using the mark length recording method by making linearly polarized light polarized in a direction perpendicular to the track direction, and recording information with a larger recording capacity per layer and a larger number of layers. When reproducing information from a medium, an optical information recording and reproducing apparatus capable of reducing diffraction loss in each recording layer to improve transmittance and reproducing each recording layer with a good SN ratio can be provided.

(Embodiment 2)

Next, the optical information recording and reproducing apparatus of Embodiment 2 of the present invention will be described focusing on the differences from the optical information recording and reproducing apparatus described in Embodiment 1 using FIG. 6.

Fig. 6 is a schematic diagram showing the basic configuration of the optical information recording and reproducing apparatus according to the present embodiment and the state in which light is propagated.

The optical information recording and reproducing apparatus of the present embodiment includes a light source 24 that emits light 25 as recording light or reproduction light, and light 25 that is emitted from the light source 24 in the information recording medium 21. The objective lens 6 condensing on any one of the plurality of recording layers 1a to 1d, and the first light detector 19a and the second detecting the reflected light 17a and 17b from the information recording medium 21. The photodetector 19b is provided. In addition, in order to guide the light 25 emitted from the light source 24 to the objective lens 6, the collimator lens 16, the beam splitter 26, the granular mirror 12, and the spherical aberration correcting element 13 are provided. It is installed. Between the beam splitter 26, the first photodetector 19a and the second photodetector 19b, the diffraction type focus / track error signal detection element 15 and the detection lens 11 are similar to those of the first embodiment. And a pinhole plate 14 having at least one pinhole. In the present embodiment, the converged light 7 irradiated onto the information recording medium 21 is linearly polarized light which is polarized in a direction perpendicular to the track direction of the information recording medium 21. In addition, since the same code | symbol is attached | subjected to the apparatus demonstrated in Embodiment 1, since it is a member which has the same function, the detailed description is abbreviate | omitted here. In addition, when the information is recorded on the information recording medium 21, the mark length recording method is used, the shape of the recording mark, and the like are the same as those in the first embodiment.

The optical information recording and reproducing apparatus of the present embodiment differs from the apparatus described in the first embodiment by using a semiconductor laser light source that emits linearly polarized light having a wavelength of 0.405 µm as the light source 24, for example. It is used as both a dragon and a regenerative light. The light source 24 emits a laser light having a high peak power by pulse oscillation during recording, and emits a laser light having a low peak power by continuous oscillation during reproduction. In this configuration, since only one light source is required, the configuration is simplified. In addition, by using the semiconductor laser light source as the light source 24, the size and cost can be reduced. Further, the semiconductor laser light source is set so that the polarization state of the emitted linearly polarized light is polarized in a direction perpendicular to the track direction.

The beam splitter 26 is not a polarizing beam splitter but a half mirror that does not depend on the polarization direction. Accordingly, the wavelength plate is also unnecessary, and the light utilization efficiency is reduced by that amount, but the effect of birefringence that may occur in the information recording medium 21 can be reduced.

 By using the above linearly polarized light as the reproduction light, as in the case of the optical information recording and reproducing apparatus of the first embodiment, the diffraction loss in each recording layer is reduced to improve transmission efficiency, and each recording layer is reproduced with a good SN ratio. It is possible to provide an information recording and reproducing apparatus corresponding to an information recording medium having a large recording capacity per layer and a large number of layers. In addition, in this embodiment, although linearly polarized light was used as the reproduction light irradiated to the information recording medium 21, an ellipse including as a main component a polarization component that polarizes in a direction perpendicular to the track direction of the information recording medium 21. The same effect can be obtained also when polarized light is used.

The objective lens, collimator lens, and detection lens used in the optical information recording and reproducing apparatuses of the first and second embodiments described above are named for convenience and are the same as the lenses generally mentioned.

In the optical information recording and reproducing apparatuses of the first and second embodiments described above, an optical disk is used as an example of an information recording medium. However, the optical information recording and reproducing apparatus is not limited thereto, and the optical information recording and reproducing apparatus is not limited thereto. Inclusion of a drum-shaped and tape-shaped product as an information recording medium is also included in the scope of the present invention.

According to the optical information recording and reproducing apparatus of the present invention, with respect to an information recording and reproducing apparatus including an information recording medium having a plurality of recording layers in which information is recorded by the mark length recording method, the transmittance is reduced by reducing the diffraction loss in each recording layer. The recording layer can be reproduced with a good SN ratio. In addition, since the diffraction loss can be reduced, it is also possible to increase the number of stacked layers of the recording layer, thereby further increasing the capacity.

Claims (19)

It is possible to record information three-dimensionally, and a track having a predetermined track pitch is provided, and includes a recording unit having a recording layer of a multi-layer structure, and a plurality of tracks along the tracks of the recording unit in a mark length recording method. In the case where the recording mark is formed, the information is recorded, and in the case where the track direction is set to the longitudinal direction with respect to the recording mark and the direction perpendicular to the track direction is set to the transverse direction, in the recording mark positioned substantially on the same plane, An information recording medium having a larger total area of a recording mark having a shape having a longer longitudinal length than a transverse length having a longitudinal length larger than a total area of a recording mark having a shape other than the shape having a longer longitudinal length; A first semiconductor laser light source that emits regenerated light having a wavelength λ ₁ ; An objective lens for condensing the reproduction light emitted from the first semiconductor laser light source by passing another recording layer through a predetermined recording layer of a recording unit of the information recording medium; An optical information reproducing apparatus, comprising: a first optical detector for receiving reflected light from the predetermined recording layer of the recording unit to detect a reproduction signal; The track pitch of the information recording medium is 1.3 times or less the wavelength λ _{1 of} the reproduction light, As the first semiconductor laser light source, a semiconductor laser light source that emits a reproduction light larger than another polarization component whose amplitude of the polarization component to be polarized in a direction perpendicular to the track direction is disposed, or An optical component for converting the polarization state of the reproduction light emitted from the first semiconductor laser light source in the optical path between the first semiconductor laser light source and the objective lens, and condensing on the predetermined recording layer of the recording unit; The amplitude of the polarization component which polarizes in the direction perpendicular | vertical to the said track direction in light is made larger than other polarization components, The optical information reproduction apparatus characterized by the above-mentioned. The method of claim 1, And the reproducing light focused on the recording unit is linearly polarized light which polarizes in a direction perpendicular to the track direction of the information recording medium. The method of claim 1, And an elliptically polarized light whose amplitude of the polarized light component polarized in the direction perpendicular to the track direction of the information recording medium is greater than other polarized light components. The method of claim 1, The optical information reproducing apparatus, wherein the first semiconductor laser light source further emits recording light having a wavelength λ ₂ . The method of claim 1, An optical information reproducing apparatus, further comprising a second light source for emitting the recording light of the wavelength [lambda] ₂ . The method of claim 5, And the second light source is a semiconductor laser. The method according to claim 4 or 5, The objective lens condenses the recording light onto a recording unit included in the information recording medium, and the recording light condensing on the recording unit is polarized with a different amplitude of polarization component to polarize in a direction perpendicular to the track direction of the recording unit. An optical information reproducing apparatus larger than the component. The method of claim 5, The objective lens focuses the recording light on a recording unit included in the information recording medium, and the wavelength λ _{1 of} the reproduction light and the wavelength λ ₂ of the recording light are different from each other, And the polarization component polarized in the direction perpendicular to the track direction of the recording unit is larger than other polarization components, and the recording light focused on the recording unit is circularly polarized. In an optical path between a semiconductor laser light source and the objective lens, an optical for converting the polarization state of the reproduction light emitted from the first semiconductor laser light source and the polarization state of the recording light emitted from the first semiconductor laser light source or the second light source. An optical information reproducing apparatus, further comprising a component. The method of claim 8, The optical component is substantially functions as a plate integral multiple of λ _1/2 with respect to the reproducing light, and also a wave plate, an optical information reproducing apparatus that substantially functions as the λ _2/4 plate with respect to the recording light. The method according to claim 4 or 5, An optical information reproducing apparatus, wherein the wavelength [lambda] _{1 of} the reproduction light is shorter than the wavelength [lambda] ₂ of the recording light. The method according to claim 4 or 5, The recording light is pulsed light, and information recording is performed by using a nonlinear absorption phenomenon. The method of claim 1, And a pinhole plate having a pinhole through which light reflecting information of a purpose contained in the reflected light is disposed in an optical path between the information recording medium and the first photodetector. The method of claim 1, An optical information reproducing apparatus, wherein the area of the light receiving portion provided in the first photodetector is set to an area for receiving light that reflects the target information contained in the reflected light. The method of claim 12, A second photo detector for detecting a focus / track error signal, and a focus / track error signal detecting element for splitting the reflected light, disposed in an optical path between the information recording medium and the second photo detector, At least one branched light branched to the focus / track error signal detecting element is guided to the second photodetector without passing through the pinhole. The method of claim 1, And the recording mark is void. The method of claim 1, The recording mark is an optical information reproducing apparatus, which is a recording pit due to a change in refractive index. delete delete delete

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